Glass sheets and other substrates can be coated with a stack of transparent, metal-containing films to vary the optical properties of the coated substrates. Particularly desirable are coatings characterized by their ability to readily transmit visible light while minimizing the transmittance of other wavelengths of radiation, especially radiation in the infrared spectrum. Known coatings that reflect infrared radiation include low-emissivity coatings and also transparent conductor coatings, such as indium tin oxide (“ITO”) coatings. These coatings are useful for reducing radiant heat transfer without impairing visible transmittance. Coated glass of this nature is useful as architectural glass and as automotive glass.
Coated glass sheets are often incorporated into glazings. At least three types of glazings are commercially available today. These three types are often referred to as single glazing, double glazing and triple glazing. Double glazings are the most common. They commonly include an insulating glazing unit (“IG unit”) having a sealed space between two panes of glass. Coating on the glass imparts desirable optical properties into the glazing.
It is challenging to provide a glazing that exhibits a well balanced set of properties. For example, when a glazing includes a glass sheet bearing a coating, such as a low-emissivity coating, it is challenging to achieve a desired level of visible transmittance, low visible reflectance, good thermal insulating properties, neutral color, and good durability. In particular, it is difficult to identify specific combinations of film thicknesses and compositions that achieve an exceptional balance of coating properties. To achieve exceptional results for a particular property, one may consider a variety of potential coating adjustments. Many adjustments, however, adversely impact other desired coating properties.
It is also challenging to provide coated glass that can be produced in a cost-effective manner. For example, transparent conductor coatings, such as ITO coatings, can be expensive to produce. Materials for producing ITO coatings are also limited in supply. As a result, there is a need for an alternate transparent conductor coating in the marketplace. ITO coatings also may have less than desirable durability. For example, ITO coatings may be relatively prone to scratching. Thus, there is a need for a transparent conductor coating that can be produced in a cost-effective manner and also is durable.
Desirable properties are even more difficult to achieve when coatings are subjected to heat treatment. It is often necessary to heat coated glass sheets to temperatures at or near the melting point of glass to temper the glass or to enable it to be bent into desired shapes, such as curved automobile windshields. Tempering is important for glass in automobile windows, and particularly for glass in automobile windshields. Upon breaking, tempered glass desirably exhibits a break pattern in which the glass shatters into a great many small pieces, rather than into large dangerous shards. During tempering, coated glass is typically subjected to elevated temperatures on the order of about 700 degrees C. Moreover, coated glass often must be able to withstand such temperatures for substantial periods of time. Certain coatings, for example ITO coatings, may not withstand such high temperature processing without some deterioration. Thus, there is a need for a transparent conductor coating that can withstand high temperature processing.
Some glazings include laminated glass assemblies. Laminated glass assemblies typically include two panes of glass laminated together by a polymer interlayer. One limitation of conventional laminated glass assemblies resides in the strength of the polymer interlayers. In some cases, the interlayer may break down over time so that the adhesion between the panes also breaks down. Polymer interlayers are often thick so they can resist breaking down over time. It would be desirable to provide thinner and/or higher strength laminated glass assemblies. It would also be desirable to provide laminated glass assemblies with an interlayer that is both highly resistant to breaking down over time and durable to elevated temperatures.